If you are a SNCO then a letter to the RSM is the form. If you are a JNCO then an email might be ok, but what's wrong with an old fashioned phone call. You can introduce yourself, explain why you are calling and if he/she needs any more gen then an email can follow.
RAWO dit -[or Chief Clerk as they were in them days] as a full screw I was on leave/OU summer school before joining a new unit - I got a 'life and death' message to contact the CC at my new unit, Family Tragedy? Emergency Deployment - quite possible at the time? Fire, Flood, Pestilence?.....turned out we knew each other very well and he'd brought my posting forward a week so I could get myself to Aldershot for an Army Cup cricket match. Useful folk to get on well with - give them a call.